Penicillin-binding proteins (PBPs) are a group of proteins characterized by their affinity for and binding of penicillin. PBPs do not just bind penicillin, but rather bind all beta-lactam antibiotics, which are a family of antibiotics sharing a four membered lactam ring.
There are a large number of PBPs, usually several in each organism, and they are found mostly as membrane-bound proteins, but a few are known to be non-membrane associated. Different PBPs occur in different numbers per cell and have varied affinities for different kinds of β-lactam antibiotics. PBPs are involved in the final stages of the synthesis of peptidoglycan, which is the major component of bacterial cell walls. Bacterial cell wall synthesis is essential to growth, cell division (thus reproduction), and maintenance of the cellular structure in bacteria. Inhibition of PBPs leads to irregularities in bacterial cell wall structure such as elongation, lesions, loss of selective permeability, and eventual cell death and lysis. Bacterial cell wall synthesis, and in particular PBPs, provides a good target for drugs of selective toxicity because the metabolic pathways and enzymes are unique to bacteria.